黑土颗粒有机碳和氮含量对有机肥剂量响应的定量关系

黑土是一种非常重要的耕种土壤,但是由于过度地开发利用和水土流失导致土壤有机质含量迅速下降,严重影响了耕地生产力和作物产量。为了能够快速恢复黑土肥力,利用海伦国家野外科学观测研究站内的长期定位试验,定量分析了黑土颗粒有机碳和氮含量对有机肥剂量的响应。田间试验开始于2001年,设置了4个施肥处理,分别为:1单施化肥(OM0);2低剂量有机肥与化肥配施(OM1);3中剂量有机肥与化肥配施(OM2);4高剂量有机肥与化肥配施(OM3)。在2011年播种前,采集各处理0~20 cm耕层土壤样品。应用有机碳物理分组方法,测定分析了土壤有机碳、氮及各组分的含量。研究结果表明长期不同剂量有机肥输入能够显著增加黑土总有机碳和全氮含量(P0.05),每增施1 t有机肥,土壤有机碳含量增加0.186 kg,土壤全氮含量增加0.02 kg,表明增加有机肥投入量是提高黑土有机碳含量的有效措施。有机肥的施用增加了土壤中粗颗粒和细颗粒组分,不同剂量有机肥处理表现为OM3OM2OM1OM0,而减小了土壤中矿质结合态组分的含量;随着有机肥施入量的增加,粗颗粒和细颗粒土壤有机碳和氮的含量呈增加的趋势,而矿质结合态中的有机碳含量则略有下降,表明粗颗粒和细颗粒有机碳和氮是黑土有机碳和氮的主要储存库,有机无机配施对土壤有机碳、氮的提升作用主要集中于对活性组分颗粒有机质的形成和积累。与OM0处理相比,有机肥的施入显著降低了颗粒有机质和矿质结合态有机质的C/N,并且随着有机肥施入量的增加而逐渐降低。与单施化肥相比,化肥有机肥配施能够显著增加土壤的总有机碳,全氮,颗粒有机碳、氮含量,其中以化肥配施高剂量有机肥效果最佳,有利于黑土土壤肥力的快速提升,改善黑土的土壤质量。     

Soil organic matter distribution and microaggregate characteristics as affected by agricultural management and earthworm activity

Stable microaggregates can physically protect occluded soil organic matter (SOM) against decomposition. We studied the effects of agricultural management on the amount and characteristics of microaggregates and on SOM distribution in a marine loam soil in the Netherlands. Three long‐term farming systems were compared: a permanent pasture, a conventional‐arable system and an organic‐arable system. Whole soil samples were separated into microaggregates (53–250 µm), 20–53 µm and < 20 µm organo‐mineral fractions, sand and particulate organic matter, after complete disruption of macroaggregates. Equal amounts of microaggregates were isolated, irrespective of management. However, microaggregates from the pasture contained a larger fraction of total soil organic C and were more stable than microaggregates from the two arable fields, suggesting greater SOM stabilization in microaggregates under pasture. Moreover, differences in the relative contribution of coarse silt (> 20 µm) versus fine mineral particles in the microaggregates of the different management systems demonstrate that different types of microaggregates were isolated. These results, in combination with micromorphological study of thin sections, indicate that the great earthworm activity under permanent pasture is an important factor explaining the presence of very stable microaggregates that are relatively enriched in organic C and fine mineral particles. Despite a distinctly greater total SOM content and earthworm activity in the organic‐ versus the conventional‐arable system, differences in microaggregate characteristics between both arable systems were small. The formation of stable and strongly organic C‐enriched microaggregates seems much less effective under arable conditions than under pasture. This might be related to differences in earthworm species' composition, SOM characteristics and/or mechanical disturbance between pasture and arable land.     

Carbon storage in loess derived surface soils from Central Germany: Influence of mineral phase variables

The influence of the soil mineral phase on organic matter storage was studied in loess derived surface soils of Central Germany. The seven soils were developed to different genetic stages. The carbon content of the bulk soils ranged from 8.7 to 19.7 g kg^—1. Clay mineralogy was confirmed to be constant, with illite contents > 80 %. Both, specific surface area (SSA, BET‐N₂‐method) and cation exchange capacity (CEC) of bulk soils after carbon removal were better predictors of carbon content than clay content or dithionite‐extractable iron. SSA explained 55 % and CEC 54 % of the variation in carbon content. The carbon loadings of the soils were between 0.57 and 1.06 mg C m^—2, and therefore in the ”︁monolayer equivalent” (ME) level. The increase in SSA after carbon removal (ΔSSA) was significantly and positively related to carbon content (r² = 0.77). Together with CEC of carbon‐free samples, ΔSSA explained 90 % of the variation in carbon content. Clay (< 2 μm) and fine silt fractions (2—6.3 μm) contained 68—82 % of the bulk soil organic carbon. A significantly positive relationship between carbon content in the clay fraction and in the bulk soil was observed (r² = 0.95). The carbon pools of the clay and fine silt fractions were characterized by differences in C/N ratio, δ¹³C ratio, and enrichment factors for carbon and nitrogen. Organic matter in clay fractions seems to be more altered by microbes than organic matter in fine silt fractions. The results imply that organic matter accumulates in the fractions of smallest size and highest surface area, apparently intimately associated with the mineral phase. The amount of cations adhering to the mineral surface and the size of a certain and specific part of the surface area (ΔSSA) are the mineral phase properties which affect the content of the organic carbon in loess derived arable surface soils in Central Germany most. There is no monolayer of organic matter on the soil surfaces even if carbon loadings are in the ME level.     

Assessment of the mobility and time of renewal of the densimetric fractions of organic matter in chestnut soils from the ratio of stable carbon isotopes

The results of experimental studying of the organic matter status in soils using methods of granulodensimetric fractionation and the geochemistry of the stable carbon and nitrogen isotopes are presented. The organic and organomineral matter in chestnut soils representing a chronoseries—stages of natural changes in the vegetation with different carbon isotope compositions—were investigated. The organomineral fractions and fractions of free organic matter were distinguished, the changes in their proportion due to the changes in the vegetation were analyzed, and the residence time of the carbon in the organic matter of the fractions was assessed.     

Soil management modifies micro-scale abundance and function of soil microorganisms in a Mediterranean ecosystem

The present study tests whether soil management (tillage and fertilizer) modified the small-scale abundance and function of soil microorganisms in response to changes in organic matter quantity and quality. The experimental field, located in the coastal hills of Marche (central Italy), was planted in rotation with Triticum durum in winter and Zea mais in summer. Soil samples were collected in the maize-field soil, in conventional and no-tillage (NT) systems, and in fertilized and unfertilized soil. We analysed total organic C (TOC), total nitrogen (TN) microbial biomass C (MBC), enzymes involved in C- (β-glucosidase, α-glucosidase, β-cellobiohydrolase, β-xylosidase), N- (leucine-aminopeptidase and N-acetyl-β-glucosaminidase), P- (acid phosphatase) and S-cycling (arylsulphatase), as well as functional diversity in the bulk soil, coarse sand, fine sand, silt and clay fractions. Micro-scale investigations revealed great microbial abundance in smaller fractions because of protection offered by microaggregates, whereas the distribution of enzymes reflected the availability of their corresponding substrates. No-tillage treatment significantly increased organic input, mainly in the coarser fractions, enhancing enzyme activities and the functional diversity of the microbial community. This effect was even larger in the absence of fertilizer. At the particle-size level of resolution, adding fertilizer stimulated nutrient cycling. Our results confirmed the hypothesis that no-tillage enlarges the content of particulate organic matter in the coarse sand fraction and stimulates microbial decomposition. In the smaller fractions the enlarged microbial pool and increased soil organic matter with small C/N ratio under NT confirm that this management practice is effective in increasing soil C sequestration capacity.     

Variation in amounts of carbon and nitrogen associated with particle size fractions of soils from the Palace Leas meadow hay plots

An increase in carbon (C) content of one of the more acid Palace Leas meadow hay plots (pH 4.0) is shown to occur in the >63 pm size fraction, while there is a reduction in organic matter associated with clay size fraction relative to a less acid plot (pH 5.8). Total nitrogen (N) content also is higher on the more acid plot, but the increase is smaller than for carbon, and leads to a wider overall C:N ratio in the acid plot. The lower N accumulation in the more acid plot is due to the relative increase in coarse (> 2 mm) organic matter, with a high C:N ratio. The technique used for separation of the particle size fractions does not involve removal of coarse organic matter (> 2 mm) or drying of the soil. In the grassland soils studied, coarse organic matter is a significant component (up to 13%) of total C, yet this fraction is frequently removed before analysis. By not drying the soil, separation into particle size fractions is facilitated.     

Phospholipid fatty acid profiles and xylanase activity in particle size fractions of forest soil and casts of Lumbricus terrestris L. (Oligochaeta,Lumbricidae)

Earthworms are key agents in organic matter decomposition, as they remove surface plant litter material and mix it with mineral soil. Plant litter material is comminuted in the gizzard of anecic earthworms and this is enhanced if sand particles are available. We hypothesize that this comminution of soil and litter will result in changes in the distribution of soil organic matter and soil microorganisms in the different particle-size fractions. We investigated soil organic matter content, xylanase- and microbial activity and community structure in bulk soil and particle size fractions of Lumbricus terrestris L. casts and in soil with and without the addition of beech litter.Earthworm gut passage did not affect the particle-size distribution but the content of soil organic matter was decreased in the fine sand fraction in treatments without litter (−6.80%) and increased in treatments with litter (+33.23%). The soil organic matter content of the clay fraction tended to be higher in earthworm casts. Xylanase activity was at a maximum in the fine sand fraction, lower in the coarse sand fraction and at a similar minimum in the silt- and clay-sized fraction. In the coarse sand fraction of the cast and litter treatments xylanase activity was increased by 39.1% and 124.8%, respectively. In the silt-sized fraction of casts the addition of litter increased xylanase activity (+58.6%) whereas, in casts without litter it was decreased (−36.25%). In the particle size fractions of casts, the content of bacterial PLFAs was decreased in the fine sand fraction and tended to be decreased in the clay fraction compared to the respective fractions in soil. In the silt fraction the fungal-to-bacterial PLFA ratio was higher in casts than in soil.We conclude that earthworms stabilize soil organic matter in cast aggregates predominantly by increasing the soil organic matter content in the clay fraction where it becomes protected against microbial attack. Organic matter in the coarse and fine sand fractions is decomposed primarily by fungi; xylanase is very active in these sand fractions and incorporation of litter into these fractions by the earthworms increased fungal biomass. Comminution of litter during passage through the earthworm gut increased the biomass and activity of fungi also in the silt fraction. The use of PLFA profiles in combination with other quantitative microbial methods improves the understanding of stabilizing and mobilizing processes in earthworm casts.     

Sources and composition of soil organic matter fractions between and within soil aggregates

It is generally accepted that particulate organic matter derives from plants. In contrast, the enriched labile fraction is thought by many to derive from microbes, especially fungi. However, no detailed chemical characterization of these fractions has been done. In this study, we wanted to assess the sources (plants or microbes; fungi or bacteria) and degree of microbial alteration of (i) three particulate organic matter fractions – namely the free light fraction (1.85 g cm^?3), the coarse (250–2000 μm) and the fine (53–250 μm) intra‐aggregate particulate organic matter fractions – and of (ii) three density fractions of fine‐silt associated carbon – namely < 2.0, 2.0–2.2 (i.e. enriched labile fraction) and > 2.2 g cm^?3– by analysing the amino sugars, by CuO oxidation analyses, and by ¹³C‐, ¹H‐ and ³¹P‐NMR analyses. Macroaggregates (250–2000 μm) were separated by wet‐sieving from a former grassland soil now under a no‐tillage arable regime. The three particulate organic matter fractions and the three density fractions were isolated from the macroaggregates by a combination of density flotation, sonication and sieving techniques. Proton NMR spectroscopy on alkaline extracts showed that the enriched labile fraction is not of microbial origin but is strongly degraded plant material that is enriched in aliphatic moieties partly bound to aromatics. In addition, the enriched labile fraction had a glucosamine content less than the whole soil, indicating that it is not enriched in carbon derived from fungi. Decreasing yields of phenolic CuO oxidation products and increasing side‐chain oxidation in the order coarse intra‐aggregate particulate organic matter < fine inter‐aggregate particulate organic matter < fine‐silt fractions indicate progressive alteration of lignin as particle size decreases. The light fraction was more decomposed than the coarse inter‐aggregate particulate organic matter, as indicated by (i) its larger ratio of acid‐to‐aldehyde of the vanillyl units released by CuO oxidation, (ii) the smaller contribution of H in carbohydrates to total extractable H as estimated by ¹H‐NMR spectroscopy, and (iii) a larger contribution of monoester P to total extractable P in the ³¹P‐NMR spectra. In conclusion, the four fractions are derived predominantly from plants, but microbial alteration increased as follows: coarse inter‐aggregate particulate organic matter < light fraction ≈ fine inter‐aggregate particulate organic matter < enriched labile fraction.     

封育对沙质草甸土壤理化性状的影响

对不同封育年限沙质草甸自然恢复过程中土壤理化性状进行了测定和分析。结果表明,封育对沙质草甸土壤理化性状的改善有明显的促进作用。随封育时间的延长,土壤颗粒组成发生明显变化,>0.25 mm的中粗沙成分明显减少,0.05~0.25 mm的细沙成分明显增加,而且表层粘粉粒含量也明显增加;各取样层次土壤有机碳和全氮含量在不同封育状况下形成显著差异,并随封育时间的延长而显著提高;随封育时间的延长,土壤容重逐渐减小,土壤硬度逐渐增大。相关分析表明,土壤有机碳含量、全氮含量与0.25~0.05 mm的细沙含量及<0.05mm的粘粉粒含量表现出显著的正相关关系,而与>0.25 mm的中粗沙含量呈显著的负相关关系。     

Influence of soil properties on the aggregation of some Mediterranean soils and the use of aggregate size and stability as land degradation indicators

Soil aggregation in relation to other soil properties was studied along a climatological transect in the Southeast of Spain. Three sites were selected along this transect ranging from semiarid to subhumid climatological conditions. The aggregate size distribution, the macro and microaggregate stability of the superficial soil horizon and their relations with other soil properties were analysed. Large aggregates (>10, 10–5, 5–2 mm) were present in highest proportions in the most arid of the studied areas. These large aggregates were associated with high values of water-stable microaggregates; however, they did not improve soil structure and are related to high bulk densities and low water retention. Aggregates 1–0.105 mm were positively correlated to medium, fine, very fine sand and silt fractions and to organic matter. Aggregates <0.105 mm were positively correlated to organic matter and clay content. Small aggregate sizes (1–0.105 and <0.105 mm) had a positive influence on soil water retention and they seem a good indicator of soil degradation.Water stability of microaggregates showed a positive correlation with clay content while the stability of the macroaggregates depended on the organic matter content when the organic matter content was greater than 5 or 6%. Below that threshold the carbonate content was strongly correlated with aggregate stability. A general conceptual scheme of associations between aggregate size distribution, water-stable microaggregation and textural characteristics for the area was developed.The land use history affecting soil overlaps the pattern of climatological situations and has to be taken into account. Aggregate size distribution and stability can be used as indicator of soil degradation, but not as a unique parameter.     

长期施肥土壤不同粒径颗粒的固碳效率

【目的】探讨不同施肥措施土壤有机碳在不同粒级颗粒中的分配及变化情况,可揭示各级颗粒中有机碳与外源有机碳输入之间的定量关系。【方法】依托南方红壤连续20年长期定位施肥试验,依据外源有机碳累积输入梯度选择不施肥(CK)、氮磷钾化肥配施(NPK)、氮磷钾化肥与秸秆配施(NPKS)、轮作条件下氮磷钾化肥与有机肥配施(NPKMR)、氮磷钾化肥与有机肥配施(NPKM)、单施有机肥(M)、增量氮磷钾化肥与增量有机肥配施(1.5NPKM)7个处理,并采用物理分组方法将土壤颗粒分为砂粒(53~2000μm)、粗粉粒(5~53μm)、细粉粒(2~5μm)和粘粒(2μm)4个组分。【结果】与不施肥相比,长期施肥均能显著增加土壤总有机碳及各级颗粒中的有机碳的储量,其中以施用有机肥的效果最明显。不同施肥处理各级颗粒中以粘粒的有机碳储量最高,平均为16.26 t/hm~2。施用有机肥和秸秆还田均能显著增加砂粒中有机碳的分配比例,降低粘粒有机碳的分配比例而对粗粉粒和细粉粒无显著影响。土壤砂粒所占的质量百分比及其与粗粉粒、细粉粒和粘粒的比值均与粗粉粒、细粉粒和粘粒组分中有机碳的浓度呈显著正相关关系表明小颗粒(粗粉粒、细粉粒和粘粒)中有机碳的固持和富集促进了大颗粒(砂粒)的形成与稳定。各级颗粒之间,施用有机肥处理的土壤粘粒组分的固碳速率最快,为0.29~0.52 t/(hm~2·a),其次为砂粒[0.30~0.40 t/(hm~2·a)]而粗粉粒和细粉粒的固碳速率基本相当为0.09~0.16t/(hm~2·a)。分析结果还表明土壤总有机碳及各级颗粒有机碳与外源有机碳的输入呈显著正线性相关关系,其中土壤总固碳效率为10.57%而各级颗粒之间,粘粒和砂粒组分的固碳效率(4.25%和3.60%)相当于粗粉粒和细粉粒(1.73%和1.00%)的2倍以上。【结论】南方红壤各级颗粒中有机碳均没有出现饱和现象,有机碳主要在土壤粘粒和砂粒组分中富集,细颗粒中有机碳的富集会促进大粒径土壤颗粒的形成而粘粒是土壤固碳效率最重要的矿物颗粒组成部分。表明长期配施有机肥不仅是红壤有机质提升的重要措施,也是改善红壤结构的重要途径。     

A 13C-NMR study on the formation of soil organic matter from grass residues

The development of C-distribution on functional groups in soil organic matter (SOM) was investigated in whole soil samples and organomineral particle-size fractions from the 34-year-old pot experiment Hu3-Loamy marl at Rostock. CPMAS-¹³C-NMR spectra of grass roots and whole soil samples indicated the enrichment of carboxyl-C, aliphatic C and aromatic C in SOM, Only minor changes were observed in the SOM-C distribution on functional groups between 13th and 34th experimental year. The investigation of organomineral clay and silt-size fractions showed a specific retention of aliphatics in clay. The most obvious changes in organic matter composition in size-fractions were the increase of carbohydrate-C and decrease of aromatic C.     

菜地土壤有机碳分级以及总量变化的动态特征研究

Fertilisers significantly affect crop production and crop biomass inputs to soil organic carbon（SOC）. However, the long-term effects of fertilisers on C associated with aggregates are not yet fully understood. Based on soil aggregate and SOC fractionation analysis, this study investigated the long-term effects of organic manure and inorganic fertilisers on the accumulation and change in SOC and its fractions, including the C concentrations of free light fraction, intra-aggregate particulate organic matter（POM） and intra-aggregate mineral-associated organic matter（MOM）. Long-term manure applications improved SOC and increased the concentrations of some C fractions. Manure also accelerated the decomposition of coarse POM（cPOM） into fine POM（fPOM） and facilitated the transformation of fPOM encrustation into intra-microaggregate POM within macroaggregates. However, the application of inorganic fertilisers was detrimental to the formation of fPOM and to the subsequent encrustation of fPOM with clay particles, thus inhibiting the formation of stable microaggregates within macroaggregates. No significant differences were observed among the inorganic fertiliser treatments in terms of C concentrations of MOM, intra-microaggregate MOM within macroaggregate（imMMOM） and intra-microaggregate MOM（imMOM）. However, the long-term application of manure resulted in large increases in C concentrations of MOM（36.35%）, imMMOM（456.31%） and imMOM（19.33%） compared with control treatment.     

Influence of fertilization and organic amendments on organic‐carbon fractions in Heilu soil on the loess plateau of China

The influence of fertilization on organic‐carbon fractions separated by density and particle size in Heilu soil (Calcic Kastanozems, FAO) was investigated in a 20‐year (1979–1999) long‐term experiment on the Loess Plateau of China. Compared to an unfertilized treatment, N application alone did not increase total organic carbon (TOC) and its fractions of density and particle size. However, the treatment of N + P fertilization significantly increased salty‐solution–soluble organic carbon (SSOC), microbial biomass C (MB‐C), and organic C associated with fine silt. When manure was applied alone and in combination with N and P fertilizer, the light fraction of organic C (LFOC), SSOC, and MB‐C were increased significantly, and the TOC was as high as that of a native Heilu soil. Organic C associated with different particle‐size fractions was also increased significantly, and the allocation of C among the fractions was altered: the proportions of C in sand (>50 μm), coarse‐silt (20–50 μm), and fine‐clay (<0.2 μm) fractions were increased whereas fine‐silt (2–20 μm) and coarse‐clay (0.2–2 μm) fractions were decreased. It is concluded that N fertilizer alone is not capable of restoring organic‐matter content in the Heilu soils of the Loess Plateau and that C‐containing material like manure and straw is necessary to produce significant increase in soil organic carbon in these soils.     

Content and composition of free and occluded particulate organic matter in a differently textured arable Cambisol as revealed by solid‐state 13C NMR spectroscopy

The composition of functional light soil organic matter pools of arable Cambisols with a gradient in clay content was investigated. Soil texture differences originate from increasing loess admixture to the parent material (coarse‐grained tertiary sediments). Using density fractionation in combination with ultrasonic dispersion, two types of particulate organic matter (POM) were obtained: (1) free POM and (2) POM occluded in soil aggregates. Both POM fractions were analyzed by elemental analysis (C, N) and CPMAS ¹³C NMR spectroscopy. With increasing clay content the amount of organic carbon stored in the occluded POM fraction increased considerably, whereas the amounts of free POM were not related to the soil clay content. With increasing soil clay contents increasing proportions of O‐alkyl C and decreasing proportions of aryl C were found for both POM fractions. The occluded POM fraction showed a higher degree of degradation as indicated by lower amounts in O‐alkyl carbon. A lower degree of POM degradation was associated with higher clay contents. Higher soil clay contents promoted the conservation of POM with a low degree of alteration. This effect of soil texture was found to be highly significant when the aryl C : O‐alkyl C ratio was used as indicator for POM decomposition rather than the alkyl C : O‐alkyl C ratio.     

流动沙丘造林对土壤物理组分有机碳分配的影响

(1)根据中国知网(CNKI)的《中国学术期刊影响因子年报(自然科学与工程技术.2010版)计量指标统计表》,《水土保持通报》综合统计源统计的总被引频次为3 446次(2009年版中为1 358次);复合影响因子为0.955;期刊综合影响因子为0.568(2008年为0.493),在所统计     

长期施肥下灰漠土有机碳组分含量及其演变特征

采用湿筛和重液悬浮的物理分组方法分析了18年不同施肥模式下灰漠土有机碳组分含量差异及其演变特征。结果表明:与不施肥相比,长期有机无机肥配施(NPKM和1.5 NPKM)增加各有机碳组分的效果最显著,且粗和细自由颗粒有机碳、物理保护有机碳、矿物结合有机碳增加速率最高,平均分别达到0.12、0.06、0.08及0.17g/(kg.a);秸秆还田使粗和细自由颗粒有机碳分别以0.05和0.03 g/(kg.a)的速率增加,而撂荒和施化肥维持着各有机碳组分的含量。不同有机碳组分间存在显著的相关性,其中以粗自由颗粒有机碳含量增幅最高,不同施肥模式下平均增幅是其它有机碳组分的2.18~.0倍;以矿物结合有机碳所占比例最高,达到56.9%7~7.8%,说明粗自由颗粒有机碳对施肥较敏感,而矿物结合有机碳是灰漠土固存有机碳的主要形式。综上分析,长期有机无机肥配施是提高灰漠土有机碳组分含量和培肥土壤的有效模式。     

石灰性土壤团聚体中钙形态特征及其与有机碳含量的关系

本文选取5种碳酸钙含量(4.29、17.45、98.66、131.85、143.82 g/kg)差异显著的北方碱性旱地农田土壤(黑土、淡黑钙土、潮土、灰钙土和黄绵土)为研究对象,分析土壤及其各粒级团聚体中有机碳、碳酸钙和不同形态钙含量的分布特征及相关性,探讨碳酸钙对碱性旱地土壤有机碳的影响。结果表明:全土有机碳含量与碳酸钙含量之间无显著相关关系,但在0.002～0.053、<0.002 mm团聚体中二者含量显著负相关(R²分别为0.67、0.83),碳酸钙含量过高影响微团聚体有机碳积累。土壤钙形态中酸溶态和可氧化态是影响微团聚体有机碳积累的主要钙形态,全土中占全钙含量都在64.09%以上,团聚体中其含量随粒径减小而增加。钙离子是有机无机复合体的重要胶结物,但钙离子过多则可能会抢占土壤颗粒上有机碳结合点位,与黏粒和粉粒结合形成微团粒结构,影响有机碳积累。     

Aggregate-occluded black carbon in soil

The great stability of black carbon (BC) in soils may not be solely attributable to its refractory structure but also to poor accessibility when physically enveloped by soil particles. Our aim was to elucidate the intensity of physical entrapment of BC within soil aggregates. For this purpose, the A horizon of a forest, and of a grassland soil, and of three soils under tillage, were sampled at the experimental station Rotthalmünster, Germany. Black carbon was assessed in water‐stable aggregates and aggregate‐density fractions using benzene polycarboxylic acids as specific markers. The greatest BC concentrations made up 7.2% of organic carbon and were found in the < 53 μm fraction. The smallest BC concentrations occurred in the large macroaggregate fractions (> 2 mm). This pattern has been sustained even after tillage. The C‐normalized BC concentrations were significantly greater (P < 0.05) in the occluded particulate organic matter (OPOM) fractions than in the free particulate organic matter (FPOM) and the mineral fractions. This enrichment of BC compared with organic carbon in the OPOM fractions amounted to factors of 1.5–2.7. Hence, BC was embedded within microaggregates in preference to other organic carbon compounds. Only 2.5–3.5% of BC was located in the OPOM fraction < 1.6 g cm^?3, but 22–24% in the OPOM fraction with a density of 1.6–2.0 g cm^?3. This suggests that BC possibly acted as a binding agent or was selectively enriched during decomposition of protected SOM, or both. Physical inclusion, particularly within microaggregates, could therefore contribute to the long mean‐residence times of soil‐inherent BC.     

Land‐use effects on the distribution of soil organic carbon within particle‐size fractions of volcanic soils in the Transmexican Volcanic Belt (Mexico)

The aim of this study was to determine the effect of land‐use and forest cover depletion on the distribution of soil organic carbon (SOC) within particle‐size fractions in a volcanic soil. Emphasis was given to the thermal properties of soils. Six representative sites in Mexico were selected in an area dominated by Andosols: a grassland site, four forested sites with different levels of degradation and an agricultural site. Soils were fractionated using ultrasonic energy until complete dispersion was achieved. The particle‐size fractions were coarse sand, fine sand, silt, clay and particulate organic matter from the coarse sand sized fraction (POM‐CS) and fine sand (POM‐FS). Soil organic carbon decreased by 70% after forest conversion to cropland and long‐term cultivation; forest cover loss resulted in a decrease in SOC of up to 60%. The grassland soil contained 45% more SOC than the cropland one. Soil organic carbon was mainly associated with the silt‐size fraction; the most sensitive fractions to land‐use change and forest cover depletion were POM followed by SOC associated with the silt and clay‐sized fractions. Particulate organic matter can be used as an early indicator of SOC loss. The C lost from the clay and silt‐sized fractions was thermally labile; therefore, the SOC stored in the more degraded forest soils was more recalcitrant (thermally resistant). Only the transformation of forest to agricultural land produced a similar loss of thermally stable C associated with the silt‐sized fraction.